In many communication systems, a mobile communication terminal may be engaged in a communication session with a base station over a radio link whose conditions are not stable and vary over time. Occasionally, the conditions of the link deteriorate, and the reception quality at the terminal sometimes degrades to an unacceptable level, causing the communication session to drop. Additional reasons for session drop include, for example, communication protocol errors, failure in security protocols, and handover failure. In some communication systems, to prevent dropping the session, the terminal tries to retain the session by re-establishing the connection with an alternative base station with which the quality of the radio link is possibly better.
Re-establishment of data sessions is specified, for example, in Evolved Universal Terrestrial Radio Access (E-UTRA) systems, also referred to as Long Term Evolution (LTE) systems. The Third Generation Partnership Project (3GPP) E-UTRA standards specify re-establishment procedures for use by E-UTRA User Equipment (UE) and base stations (BS or eNodeB). These schemes are described, for example, in 3GPP Technical Specification 36.331, entitled “Technical Specification; LTE; Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification,” (3GPP TS 36.331 version 11.5.0 Release 11), September, 2013, and in 3GPP Technical Specification 36.304, entitled “Technical Specification; LTE; Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) procedures in idle mode,” (3GPP TS 36.304 version 11.5.0 Release 11), September, 2013, which are both incorporated herein by reference.
The description above is presented as a general overview of related art in this field and should not be construed as an admission that any of the information it contains constitutes prior art against the present patent application.